1. Field of the Invention
The present invention relates to swash plate-type compressors, and more particularly, to semispherical shoes provided between a swash plate and pistons of a swash plate-type compressor.
2. Description of Related Art
Known swash plate-type compressors are used for air conditioning systems of vehicles. Such known swash plate-type compressors may comprise a cylinder block, a front housing, and a cylinder head. The cylinder block includes a plurality of cylinder bores arranged in an annular configuration around a central axis of the cylinder block. The front housing is attached to one end surface of the cylinder block to form a crank chamber. The cylinder head is attached to another end surface of the cylinder block, via a valve plate, and forms a suction chamber and a discharge chamber. The front housing, the cylinder block, the valve plate, and the cylinder head may be attached by a plurality of bolts. The known swash plate-type compressor further comprises a drive shaft, a swash plate, a plurality of pistons, a plurality of pairs of hemispherical shoes, a suction valve, and a discharge valve. The drive shaft is supported rotatably by a central portion of the cylinder block and the front housing. The drive shaft extends through the crank chamber along a central axis of the compressor. The swash plate is mounted slidably on the drive shaft and rotates with the drive shaft. A piston is slidably positioned in each cylinder bore to reciprocate therein. Each piston includes a pair of shoe-receiving portions at one end. A pair of shoes is positioned within each pair of shoe-receiving portions. Moreover, each pair of shoes slidably contacts side surfaces of a circumferential portion of the swash plate, so that each piston is operatively connected to the swash plate by means of a pair of shoes, and so that each piston may reciprocate in a cylinder bore. The suction valve controls the introduction of a refrigerant, e.g., a refrigerant gas, to each cylinder bore. The discharge valve controls the discharge of refrigerant from each cylinder bore.
In such known swash plate-type compressors, each shoe has a substantially hemispherical configuration. Each shoe comprises a flat surface portion that contacts the swash plate, e.g., a side surface of the swash plate, and a hemispherical surface portion that contacts a shoe-receiving portion of the piston. A rectilinear chamfered portion is formed at a joint portion between the flat surface portion and the hemispherical portion.
The reciprocating components of such known swash plate-type compressors include the pistons, the shoes, and the swash plate. Thus, the inertial force of the reciprocating components during compressor operation may be proportionate to the weight of the pistons, the shoes, and the swash plate.
If such known swash plate-type compressors are variable displacement, swash plate-type compressors, the inertial force of the reciprocating components may affect the angle of inclination between the swash plate and the drive shaft during compressor operation. If a discharge capacity of the compressor is to be reduced during compressor operation, the inclination angle between the swash plate and the drive shaft may be increased. Moreover, pressure in the compressor crank chamber may be increased to increase the angle of inclination and reduce the compressor discharge capacity. However, the pressure increase in the compressor crank chamber may have to overcome an inertial force of the reciprocating components to increase the inclination angle of the swash plate. Further, the inertial force of the reciprocating components may contribute to compressor vibration during operation of swash plate-type compressors.
Therefore, a need has arisen to reduce a weight of one or more reciprocating components of swash plate-type compressors, so that the inertial force of the reciprocating components during compressor operation may be reduced. In particular, a need has arisen in variable displacement, swash plate-type compressors to reduce the weight of one or more reciprocating components, so that the discharge capacity of the compressors may be reduced more effectively. A further need has arisen to reduce the weight of one or more reciprocating components of swash plate-type compressors, so that a vibration of swash plate-type compressors may be reduced.
According to an embodiment of the present invention, a swash plate-type compressor comprises a cylinder block, a drive shaft, a swash plate, a plurality of pistons, and a plurality of pairs of shoes. The cylinder block has a plurality of cylinder bores formed therethrough. The drive shaft is rotatably supported by the cylinder block. The swash plate is mounted on the drive shaft and rotates therewith. Each of the pistons is slidably positioned within a respective one of the cylinder bores to reciprocate therein, and each of the pistons has a pair of substantially semispherical cavities formed at an end thereof. Each of the pairs of shoes is positioned between each of the plurality of pistons and the swash plate. Each shoe has a semispherical portion adapted to be positioned within one of the substantially semispherical cavities of the plurality of pistons and a flat portion slidable along a surface of the swash plate. A first concave portion is formed in the flat portion of each shoe. A second concave portion is formed in the semispherical portion of each shoe.
According to another embodiment of the invention, a compressor comprises a swash plate, a plurality of pistons, and a plurality of pairs of shoes. Each of the plurality of pistons includes a pair of substantially semispherical cavities formed at an end thereof. Each of the plurality of pairs of shoes includes a semispherical portion configured to be positioned within one of the substantially semispherical cavities of the plurality of pistons and a flat portion for contacting the swash plate. The semispherical portion of each shoe includes a first concave portion, and the flat portion includes a second concave portion.
Other objects, features, and advantages of embodiments of this invention will be understood by persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings.